Bergh ctal

ABSTRACT

CRYSTALLINE LAYERS OF GROUP III-V SEMICONDUCTOR MATERIALS ARE GROWN EPITAXIALLY FROM SOLUTION BY A METHOD WHICH INCLUDES THE ISOLATION OF SMALL EQUAL PORTIONS OF SOLUTION FROM A SOLUTION RESERVOIR. THE PORTIONS IN CONTACT WITH THE CRYSTAL SUBSTRATE ARE CONSTRAINED IN A DIRECTION PERPENDICULAR TO THE SUBSTRATE TO THE BE LESS THAN MILLIMETERS THICK BEFORE CRYSTAL GROWTH IS INITIATED BY LOWERING THE TEMPERATURE OF THE SUBSTRATE AND ITS CONTACTING SOLUTION. AT THE TERMINATION OF GROWTH, THE DEPLETED SOLUTION IS REMOVED FROM THE GROWN LAYER LEAVING A SURFACE SUFFICIENTLY PERFECT TO ALLOW FURTHER PROCESSING WITHOUT AN INTERVENING GRINDING OR POLISHING OPERATION.

AI. 27, 1974 BERGH ETAL R0.028,l40

SEIICOHDUCTOR EPITAXIAL GROWTH FROM SOLUTION Original Filqd Nov. 29.1971 F/G. IA

United States Patent Office Re. 28,140 Reissued Aug. 27, 1974 28,140SEMICONDUCTOR EPITAXIAL GROWTH FROM SOLUTION Arpad Albert Bergh, MurrayHill, Ralph Paola, Westfield, and Robert H. Saul, Scotch Plains, N.J.,assignors to Bell Telephone Laboratories, Incorporated, Murray Hill, NJ.

Original No. 3,690,965, dated Sept. 12, 1972, Ser. No. 202,837, Nov. 29,1971. Application for reissue Jan. 22, 1973, Ser. No. 325,637

Int. Cl. H011 7/38 US. Cl. 148-172 16 Claims Matter enclosed in heavybrackets II appears in the original patent but forms no part of thisreissue specification; matter printed in italics indicates the additionsmade by reissue.

ABSTRACT OF THE DISCLOSURE Crystalline layers of Group III-Vsemiconductor materials are grown epitaxially from solution by a methodwhich includes the isolation of small equal portions of solution from asolution reservoir. The portions in contact with the crystal substrateare constrained in a direction perpendicular to the substrate to be lessthan 3 millimeters thick before crystal growth is initiated by loweringthe temperature of the substrate and its contacting solution. At thetermination of growth, the depleted solution is removed from the grownlayer leaving a surface sufficiently perfect to allow further processingwithout an intervening grinding or polishing operation.

BACKGROUND OF THE INVENTION (1) Field of the invention Epitaxialcrystalline layers of Group III-V semiconductor materials are grownprimarily for light-emitting device use.

DESCRIPTION OF THE PRIOR ART The epitaxial growth of crystalline layersof Group III-V semiconductor materials has been extensively used in theproduction of such devices as light-emitting diodes. For this diodeusage the techniques mostly widely employed for this crystalline growth,involve flowing a saturated solution of the semiconductor material in ametallic solvent into contact with a crystalline substrate and reducingthe temperature of the solution-substrate system. Some of the earliesttechniques employ a rotatable furnace which was tipped in order to causethe solution to flow from one portion of the growth container intoanother portion which contains the crystalline substrate. More recentlyother techniques employing sliding members have been developed in orderto bring the saturated solution into contact with the substrate (US.Pat. Nos. 3,551,219; 3,560,276; 3,565,702).

Although layers grown by these methods are eminently suitable for manydevice uses, a recurring problem met in the growth of such crystallinelayers has been the presence of surface irregularities and solventinclusions. It is believed that these imperfections are due toconvection currents and constitutional supercooling in the melt (Minden,Journal of Crystal Growth, 6, 228 [1970] Before further processing canbe performed on such crystalline layers grinding or polishing steps areoften required. Theoretical and experimental studies of this problemhave shown that these imperfections can be suppressed somewhat bymaintaining a temperature gradient in the melt perpendicular to thesubstrate surface. Some further improvements have been realized bycoupling such a temperature gradient with a reduction in the thicknessof the solution layer. Donahue et al. (Journal of Crystal Growth,

7, 221 [1970]) report the development of a growth boat in which thesaturated solution is caused to flow into a constricted area by therotation of the boat. He reports that this constricted area cannot beless than approximately 3 mm. thick because the surface tension of thesolution prevents its flow into the constricted area. They findcrystalline surfaces produced in this boat somewhat improved, but theystill observe ripples and ridges. In spite of improvements thus farobtained, the production of epitaxial layers with more perfect surfacesis a much sought after goal.

SUMMARY OF THE INVENTION A method is presented here by which epitaxiallayers of Group III-V semiconductor materials can be grown from solutionwith surfaces smooth, uniform and reproducible enough to be suitable forfurther processing without intervening grinding or polishing operations.The method developed is adaptable to quasi-continuous production. Inthis method small portions (aliquots) of saturated solution are meteredout and isolated from a solution reservoir. Each aliquot is confined ina growth chamber in contact with the substrate to form a layer less than3 mm. thick. The epitaxial layer is then grown by temperature reduction.This temperature reduction is accomplished either by reducing thetemperature of the furnace or moving the growth chamber with itscontents into a cooler region. For better thickeness control the growthchamber is allowed to equilibrate at the lower temperature before thedepleted solution is removed from the epitaxial layer. Otherwise layergrowth is halted by the removal of the solution. Layers thus producedhave shown a high degree of smoothness, thickness uniformity andcrystalline perfection. Experimental growth systems in which thesolution layer is 1 mm. or less in thickness have produced epitaxialgrowth with nearly all of the material coming out of solution beingdeposited on the substrate (close to percent deposition efficiency).This leads to the production of epitaxial layers with a high degree ofthickness reproducibility.

BRIEF DESCRIPTION OF THE DRAWING The figure (a through c) is a series ofelevatoinal views in section of an exemplary crystal growth apparatusshowing successive steps of the growth process.

DETAILED DESCRIPTION OF THE INVENTION Solution growth The epitaxialdeposition of layers of the Group III-V semiconductor materials from ametallic solution is usually accomplished by the reduction of thetemperature of the solution below the saturation point while thesolution is in contact with a crystalline substrate. This method iswidely used in the growth of layers of materials in the galliumphosphide-gallium arsenide family. When so produced these materials aregrown from a saturated gallium solution doped with small quantities ofdonor or acceptor species or species selected to modify the luminescentproperties of the resulting layer (Casey and Trumbore, Mat. Sci. Eng.,6,69 [1970] The thickness of the grown layer depends upon the initialtemperature at which the solution is saturated, the temperature dropthrough which growth takes place, the thickness of the solution layerover the substrate and the deposition efficiency. The depositionefliciency is the relationship between the amount of dissolvedsemiconductor material which is deposited on the substrate and theamount of dissolved material which is deposited on other parts of thegrowth apparatus. It is defined as the weight of material deposited onthe substrate divided by the weight of material coming out of solution.Donor and acceptor dopants commonly used with GaP-GaAs semiconductorsinclude Zn, Se and Te.

Dopants which are sometimes included to modify the luminescentproperties of the semiconductor materials when such materials aredestined for light-emitting device use include and N. These dopants canbe dissolved in the growth solution from solid or liquid form or from agas in the system atmosphere. The amount of gallium arsenide or galliumphosphide which will be deposited from a saturated gallium solution isreadily calculatable from known data (Thurmond, J. Phys. Chem. Solids)C. (Thurmond, Journal of the Physics and Chemistry, J. Phys. Chem.Solids, 26, 785 [1965]). Table I shows the results of exemplarycalculations of the epitaxial layer thickness of gallium phosphide whichwould be deposited from a saturated gallium solution when thetemperature is reduced from the initial saturation temperature to thefinal growth temperature. The thickness calculation assumes uniformdeposition over the substrate and 100 percent deposition efliciency.Table I also indicated what percentage of all of the gallium phosphidecontained within the solution comes out of solution during deposition.

TABLE I.EPI'IAXIAL DEPOSITION OF GaP FROM Ga SOLUTION Epitaxial layerExemplary growth apparatus FIG. 1 shows an exemplary apparatus forepitaxial layer growth in accordance with the invention. In thisapparatus the measuring out and isolating of the small equal portions(aliquots) of solution is accomplished by the manipulation of slidingmembers. The solution reservoir contains a quantity of solution 11maintained at or near its saturation temperature. The reservoir 10 hasan orifice 12 at the bottom. Supported against the reservoir 10 there isan upper sliding member 13 and a lower sliding member 14. The thicknessof the upper sliding member 13 is selected to be the thickness of thealiquot desired and it is provided with an orifice 15 approximately thesame size as the substrate 16 upon which deposition is to take place.Substrate 16 lies within a depression in the lower sliding member 14with the upper surface of the substrate 16 somewhat below the plane ofthe upper surface of the lower sliding member 14. The lower slidingmember 14 is also supplied with a dump well 17 which will receive thedepleted solution after deposition. FIG. la shows the two sliders inposition below the reservoir orifice 12. The aliquot 18 is isolated fromthe reservoir by moving the two slider members 13, 14 to the right asshown in FIG. lb.

Crystal growth can be initiated in one of two ways. Either thetemperature of the whole apparatus can be reduced or the displacement ofthe upper and lower sliders 13, 14 can be such as to bring the aliquotl8 and substrate 16 to a region of lower temperature. In either case thetemperature of the aliquot and substrate 16, 18 is reduced to the finalgrowth temperature. Growth can be terminated at any time by the removalof the aliquot from contact with the substrate 16 (as illustrated inFIG. 1c) of the aliquot can be held at the final growth temperature fora sufl'icient time to allow equilibration and the deposition to reachcompletion. In either case the depleted solution is removed from contactwith the substrate 16 and its grown layer 20 by sliding the uppersliding member 13 to the left relative to the lower sliding member 14 tobring the depleted aliquot 18 over and into the dump well 17. If theclearance 21 of the upper surface of the epitaxial layer 20 is less thanapproximately 75 micrometers, the surface tension of the galliumsolution in the aliquot 18 will be sufiicient to hold the aliquottogether and result in essentially complete removal of the liquid fromthe surface of the layer 20. Other removal methods are possible such asthe use of a forceful gas stream. Equilibration in most cases isaccomplished within 15 minutes of the time that the apparatussurrounding the substrate 16 and the aliquot 18 is brought to the finalgrowth temperature.

In the quasi-continuous production process illustrated, growth of thenext epitaxial layer on the succeeding substrate 19 is initiated (FIG.ld) by moving the upper sliding member 13 further to the left, bringingthe orifice 15 in that member 13 to a position underneath the reservoirorifice 12 and over the succeeding substrate 16. If epitaxial layergrowth has been initiated by the reduction of the temperature of theentire system, the system must be brought back to the initial startingtemperature before the cycle is started again in this manner. Bysuccessive repetitions of the steps illustrated in FIGS. la through ldepitaxial layers can be grown on succeeding substrates until thesucceeding aliquots have emptied the reservoir 10 of its containedsolution 11. The apparatus can also be arranged to grow layers onseveral substrates in tandem. Epitaxial layers can be deposited on topof layer 20 by placing additional solution reservoirs to the right ofreservoir 10 and by extending the upper sliding member 13 beneath suchadditional reservoirs. The upper sliding member 13 must also includeappropriate orifices similar to orifice 15. In that case, of course, thedump well 17 must be made large enough to accommodate all of thealiquots used in the deposition of succeeding layers on substrate 16.

In addition to the advantages accruing from the use of the generalmethod outlined above, the use of each of the two principal temperaturereduction schemes, has its own particular advantage. If the temperatureof the entire apparatus is reduced in order to institute layer growth,substrate 16 need not be displaced far from reservoir 10 and a fairlycompact growth apparatus results. If the temperature reduction is to beaccomplished by removing the substrate 16 and aliquot 18 to a coolerregion of the apparatus a larger displacement is required. However, thecycling time is reduced because the reservoir 10 remains at a constanttemperature and time need not be spent waiting for the apparatus toreequilibrate at the initial starting temperature.

Examples An apparatus for layer growth in accordance with the inventionwas constructed principally of graphite and epitaxial layers of galliumphosphide were grown on gallium phosphide substrates using thetemperature reduction method in which the temperature of the entiresystem is reduced. Layers were grown using the temperatures and aliquotlayer thickness of Table II. Table II also indicates the thickness ofthe grown layer and the achieved deposition efficiency. The layersproduced in each of these examples were smooth and uniform enough forfurther processing without the requirement of grinding or polishing ofthe surface. The further processing contemplated includes the positionof additional layers, the application of electrical contacts, thediffusion of additional electrical active impurities and the applicationof photolithographic masking techniques.

It is to be noted from Table II, that, at an aliquot thickness of 3millimeters, the deposition efliciency is rapidly decreasing. Since lowdesposition elfieciency adversely affects both the economics and thereproducibility of the process, the use of aliquot thickness greaterthan 3 millimeters is not recommended. On the other hand thickness of 1millimeter or less produce essentially 100 percent deposition efiiciencyand are, thus, preferred.

What is claimed is:

1. Method for the production of a semiconductor device including theepitaxial growth of a thin crystalline layer of a semiconductor materialon a crystalline substrate from solution characterized in that themethod comprises:

(a) contacting the substrate with solution from a solution reservoircontaining a body of solution of the semiconductor materials while thesolut on reservoir is maintained at a solution temperature[,] and[(b)isolating a portion of the solution in contact with the substratewithin a growth chamber constrained] constraining a portion of the bodyof solution in the thickness direction so as to form a solution layernot greater than 3 millimeters thiok[;] in contact with the substrate;

[(c)] (b) reducing the temperature of the [growth chamber] solutionlayer to a final temperature during a growth time, during which growthtime the thin crystalline layer forms on the substrate; and

[(d)] (c) removing the depleted solution from the crystalline layer.

2. Method of claim 1 in which the growth chamber is moved away from thereservoir during the growth time so that the temperature reduction ofthe growth chamber is independent of the temperature of the reservoir.

3. Method of claim 2 in which the temperature of the reservoir remainsessentially constant at the solution temperature during the growth time.

4. Method of claim 1 in which the depleted solution is removed from thecrystalline layer while the growth chamber is at the final temperature.

5. Method of claim 4 in which the growth time is sufficiently long toallow the growth chamber and its contents to come essentially to thermalequilibrium before the depleted solution is removed.

6. Method of claim 1 in which the solution layer is not greater than 1millimeter thick.

7. Method of claim 1 in which the temperature of the solution layer isessentially uniform in the thickness direction during the growth time.

8. Method of claim [1] 16 in which the portion of the solution isisolated by moving a first slider and a second slider together relativeto the solution reservoir.

9. Method of claim 8 in which the depleted solution is removed from thecrystalline layer by moving the second slider relative to the firstslider.

10. Method of claim 9 in which the clearance between the lower surfaceof the second slider and the upper surface of the crystalline layer isless than micrometers.

11. Method of claim 8 in which the depleted solution is removed from thecrystalline layer by means of a gas stream.

12. Method of claim [1] 16 in which the thin crystalline layer iscontacted with a second solution reservoir and a second crystallinelayer is formed from a second isolated portion of solution.

13. Method of claim 1 in which an electrical contact is applied to thecrystalline layer, which crystalline layer is in the as-formed state.

14. Method of claim 1 in which photolithographic processing is performedon the crystalline layer, which crystalline layer is in the as-formedstate.

15. Method of claim 1 including contacting the substrate with thesolution reservoir and subsequently constraining the portion of the bodyof solution so as to form the solution layer.

16. Method of claim 15 including separating the portion from thesolution reservoir.

References Cited The following references, cited by the Examiner, are ofrecord in the patented file of this patient or the original patent.

UNITED STATES PATENTS 3,664,294 5/1972 Solomon l48172 X 3,692,592 9/1972Marinelli 148-l72 3,741,825 6/1963 Lockwood et al. l48l72 X 3,551,21912/1970 Parish et al. 148-171 3,560,276 2/1971 Parish et al. H l481713,565,702 2/1971 iNelson 148-472 GEORGE T. OZAKI, Primary Examiner U.S.Cl. X.R.

l48l7l, 173; 117-201; 252-623 GA UNITED STATES PATENT OFFICE CERTIFICATEOF CORRECTION Reissue xnmm 281m Dated August 227 197A n fl Amend A.Bergh, Carl R. Paola and Robert H. Saul It is certified that errorappears in the above-identified patent and that said Letters Patent arehereby corrected as shown below:

Column 1, line 5, "Ralph Paola should read --Carl Ralph Paola--.

Signed and sealed this 5th day of November 1974.

(SEAL) Attest:

McCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner ofPatents

